1. Field of the Invention
This invention relates to a system adapted to visually display digital image data and, more particularly, to a system including a failsafe mechanism adapted to visually display digital image data and a method therefor.
2. Description of the Prior Art
Digital image data is input to a system adapted to visually display digital image data on a display device. Digital image data is input to a frame locked system one frame at a time at a vertical refresh or frame rate. A frame is an image displayed for viewing on a display device or panel at one time, i.e., one frame of data fits on the display device screen or panel. Each frame includes a rectangular array of pixels. Each pixel has one or more values, for example, a gray scale luminance value for a monochrome display or red, green, and blue (RGB) luminance values for a color display. The resolution of the array, i.e., the number of horizontal and vertical pixels, is often referred to as an image frame resolution. Common display frame resolutions include that shown in Table 1 indicating, in the second and third columns, the number of pixels in the vertical and horizontal dimensions, respectively:
TABLE 1VGA640480SVGA800600XGA1024768SXGA12801024UXGA16001200HDTV1280720
Display monitors must be refreshed many times per second. The refresh rate for a display device is measured in hertz (Hz) and is also called the vertical refresh rate, vertical frequency, vertical scan rate, or frame rate. Put differently, digital image data is input at an input frame rate. An input vertical refresh or frame rate is the rate at which a frame of data is received by the system. A display vertical refresh rate is the rate at which digital image data is provided to a display device for visually displaying the input image data. Common input and display vertical refresh rates include 60, 75, and 85 Hz and the like.
Where the display vertical refresh rate and/or resolution match the input vertical refresh rate and/or resolution, the frame of image data is displayed directly without issue. If, however, the input and display vertical refresh rates and/or the resolutions differ substantially, the image data might not be properly displayed on the display device. This is particularly true in frame locked systems where small line memories are commonplace since these line memories do not allow for full conversion of the input vertical refresh rate to a vertical refresh rate that matches the display vertical refresh rate.
When the input and display vertical refresh rates differ, the display device and, more particularly, the software that drives the display device might enter an unrecoverable error mode. For example, assume UXGA image data input at 85 Hz and a VGA display running at 60 Hz. In this circumstance, the system is incapable of displaying the image data. The VGA display device might go blank except perhaps for a single line error message that reads SYNCH ERROR or OUT OF RANGE.
A system reset will not generally cure the error because the system will continue to deliver image data at a display vertical refresh rate and/or resolution that exceeds the capability of the display device. The software and/or hardware driving the display device will not give a perplexed user a way of changing its settings to ensure the error does not recur.
Accordingly, a need remains for a system including a failsafe mechanism adapted to visually display digital image data and a method therefor.